linux-kernel - Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less confusion

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Message-ID: <20240604091503.GQZl7bF14qTSAjqUhN@fat_crate.local>
Date: Tue, 4 Jun 2024 11:15:03 +0200
From: Borislav Petkov <bp@...en8.de>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	Jun Nakajima <jun.nakajima@...el.com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	"Kalra, Ashish" <ashish.kalra@....com>,
	Sean Christopherson <seanjc@...gle.com>,
	"Huang, Kai" <kai.huang@...el.com>,
	Ard Biesheuvel <ardb@...nel.org>, Baoquan He <bhe@...hat.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>, kexec@...ts.infradead.org,
	linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv11 05/19] x86/relocate_kernel: Use named labels for less
 confusion

On Mon, Jun 03, 2024 at 05:24:00PM -0700, H. Peter Anvin wrote:
> Trying one more time; sorry (again) if someone receives this in duplicate.
> 
> > > > 
> > > > diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
> > > > index 56cab1bb25f5..085eef5c3904 100644
> > > > --- a/arch/x86/kernel/relocate_kernel_64.S
> > > > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > > > @@ -148,9 +148,10 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
> > > >    	 */
> > > >    	movl	$X86_CR4_PAE, %eax
> > > >    	testq	$X86_CR4_LA57, %r13
> > > > -	jz	1f
> > > > +	jz	.Lno_la57
> > > >    	orl	$X86_CR4_LA57, %eax
> > > > -1:
> > > > +.Lno_la57:
> > > > +
> > > >    	movq	%rax, %cr4
> 
> If we are cleaning up this code... the above can simply be:
> 
> 	andl $(X86_CR4_PAE | X86_CR4_LA54), %r13
> 	movq %r13, %cr4
> 
> %r13 is dead afterwards, and the PAE bit *will* be set in %r13 anyway.

Yeah, with a proper comment. The testing of bits is not really needed.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette